Chemical substance detection apparatus and chemical substance detection method

ABSTRACT

A vacuum ultraviolet lamp ionizes a chemical substance contained in exhaust gas Gs. The chemical substance ionized is trapped in an ion trapping apparatus in which a radio frequency electric field is formed. Energy is applied to an ion group in the ion trapping apparatus with a SWIFT waveform comprising a frequency component excluding a frequency corresponding to an orbital resonance frequency of ions of the chemical substance to remove an impurity. Energy is then applied to the ion group with a TICKLE waveform having a frequency component corresponding to the orbital resonance frequency of the ions of the chemical substance to fragmentate the ions of the chemical substance. A mass of the fragment is then measured with a mass spectrometer to identify the chemical substance.

TECHNICAL FIELD

The present invention relates to a chemical substance detectionapparatus and a method for measuring a chemical substance concentration,and more particularly to a chemical substance detection apparatus and achemical substance detection method, which are used for detecting, withhigh accuracy, a dioxin or a precursor thereof contained in a veryslight amount in the exhaust gas from, for example, a refuseincineration system.

BACKGROUND ART

Recently, for reducing dioxins contained in the exhaust gas from arefuse incineration system, attempts are being made to measure in realtime dioxins or precursors thereof contained in the exhaust gas and usethe measurement values for controlling combustion of the incinerationfurnace. The dioxins may be measured with high-resolution GC/MS (gaschromatography/mass spectrometer). However, this method requirescumbersome pretreatment and, currently, a time of from sampling toobtaining a result needs several weeks so that it is not practical touse this method where real-timeness is required. An on-line monitor isknown in which dioxins or precursors thereof contained in exhaust gasare ionized by an atmospheric pressure chemical ionization method andthe resultant ions are measured by means of a three-dimensional tetrodemass spectrometer. The on-line monitor has been described in detail inAbstracts of the 11th Conference 2000 of Japan Society of WasteManagement Experts, and see the literature if necessary.

However, the atmospheric pressure chemical ionization method has thefollowing problems. First, the sensitivity for measurement of moleculeswhich are hardly changed to negative ions is low due to its measurementprinciple, and therefore the method is difficult to apply to controlwith high precision. The ionization probability of a chemical substanceto be measured is largely affected by the gas composition of anatmosphere. Thus, for determining a concentration of the chemicalsubstance from the measured electric signal intensity by makingcalculation, it is necessary to use a chemical substance containing anexpensive C isotope as an internal standard sample, increasing the costfor the measurement.

In the atmospheric pressure chemical ionization method, generally, aphenol is detected wherein there is a correlation between a phenol and adioxin with respect to the concentration and a phenol has relativelyhigh sensitivity of measurement. However, the phenol is likely to bedeposited on a pipe and therefore the memory effect is remarkable, and,for achieving a measurement with high sensitivity, piping is required tobe improved with some contrivances. In addition, even in cleaned exhaustgas, a phenol is disadvantageously detected due to the memory effect,thereby lowering the accuracy of the measurement. Further, when asubstance which is more easily ionized than the precursor to be measuredis present in the exhaust gas, such a substance is first ionized, thusmaking it difficult to accurately measure the substance to be measured.

A certain precursor (e.g., trichlorophenol), which is an optimal indexsubstance of the dioxin concentration for one furnace, is not always anoptimal index substance for another furnace since there may be adifference between the one furnace and another with respect to the typeof furnace or the conditions for combustion, and thus, the method whichcan measure a single precursor has only poor general-purpose properties.In other words, a method having improved general-purpose propertiesadvantageously can detect various types of chemical substancessimultaneously if possible.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to solve at least the problemsin the conventional technology.

A chemical substance detection apparatus according to an aspect of thepresent invention includes an ionization unit that applies to a chemicalsubstance energy higher than an ionization potential of the chemicalsubstance and lower than a sum of the ionization potential anddissociation energy of ions of the chemical substance to ionize thechemical substance; an ion trapping unit that traps, using any one of anelectric field and a magnetic field, an ion group comprising the ions ofthe chemical substance formed by ionization by the ionization unit; animpurity removing unit that applies energy to the ion group by means ofa SWIFT waveform comprising a frequency component excluding a frequencycorresponding to an orbital resonance frequency of the ions of thechemical substance to remove an impurity from the chemical substance;and a mass analyzer that measures a mass of the chemical substance.

In the chemical substance detection apparatus according to theabove-mentioned aspect, in ionization of a detection object chemicalsubstance, energy higher than an ionization potential of the detectionobject chemical substance and lower than a sum of the ionizationpotential and dissociation energy of ions of the detection objectchemical substance is applied to the detection object chemicalsubstance. Therefore, the chemical substance to be detected can beionized without being broken, making it possible to improve theionization efficiency.

Further, a SWIFT waveform is merely applied for removing an impurity andhence, the impurity can be quickly removed. In the ionization accordingto the present invention, the energy required for ionization isappropriately adjusted, and hence various molecules do not unnecessarilysuffer dissociation or ionization. Therefore, only a very few fragmentsare generated and the amount of impurities to be removed in the step ofremoving an impurity is extremely small, so that the SWIFT voltage canbe lowered to allow the chemical substance to be detected to be left toremain unbroken, making it possible to improve the detection sensitivityof the mass analyzer. In addition, there is no need to prepare anexcessively high power source and the production cost for the apparatuscan be suppressed. Further, in the chemical substance detectionapparatus according to the present invention, generation of excessivefragment ions can be considerably suppressed, thus making it possible tosuppress a lowering of the trapping efficiency caused by an excessamount of ions present in the ion trap. As the mass analyzer, it isespecially preferred to use one of a time-of-flight measurement modesince the time for measurement can be shortened. In the ion trappingunit, a unit that traps ions in the unit using an electric field, amagnetic field, or another electromagnetic force can be used. Anelectric field, a magnetic field, and other unit may be usedindividually or a plurality of these may be used in combinationappropriately. As such an ion trapping unit, an ion trap in which aradio frequency electric field is formed is known, and this is preferredbecause the handling is relatively easy (this applies to the following).

The term “detection object chemical substance” here means a precursor ofa dioxin or a dioxin contained in the exhaust gas from, for example, anincineration furnace. In the chemical substance detection apparatusaccording to the present invention, a dioxin concentration of theexhaust gas can be presumed by detecting a precursor having a goodcorrelation with a dioxin. Alternatively, a dioxin contained in theexhaust gas can be directly detected to determine the dioxinconcentration. The latter can be used for detecting a presumed value bya precursor. Dioxins generally include dioxins, furans, and moleculescalled coplanar PCB. The precursors include benzenes, such astrichlorobenzene, dichlorobenzene, and monochlorobenzene, and phenols,such as trichlorophenol.

In addition, SWIFT represents “Stored Waveform Inverse FourierTransform”. See “Development of a Capillary High-Performance LiquidChromatography Tandem Mass Spectrometry System Using SWIFT Technology inan Ion Trap/Reflectron Time-of-flight Mass Spectrometer”, RapidCommunication in mass spectrometry, vol. 11 1739–1748 (1997), fordetails.

A chemical substance detection apparatus according to another aspect ofthe present invention includes an ionization unit that applies to achemical substance energy higher than an ionization potential of thechemical substance and lower than a sum of the ionization potential anddissociation energy of ions of the chemical substance to ionize thechemical substance; an ion trapping unit that traps, using any one of anelectric field and a magnetic field, an ion group comprising the ions ofthe chemical substance formed by ionization by the ionization unit; animpurity removing unit that applies energy to the ion group by means ofa SWIFT waveform comprising a frequency component excluding a frequencycorresponding to an orbital resonance frequency of the ions of thechemical substance to remove an impurity from the chemical substance; afragmentation unit that applies energy to the ion group by means of aTICKLE waveform comprising a frequency component corresponding to theorbital resonance frequency of the ions of the chemical substance tofragmentate the ions of the chemical substance; and a mass analyzer thatmeasures a mass of a fragment of the chemical substance.

In the chemical substance detection apparatus according to theabove-mentioned aspect, fragmentation of the detection object chemicalsubstance is performed by means of a fragmentation unit that applies aTICKLE waveform. Therefore, even when an impurity is present in afrequency band corresponding to the mass number of the detection objectchemical substance, the effect of the impurity can be removed to achievean accurate measurement. In addition, only a very few fragments aregenerated in the ionization and therefore, in the fragmentation of thedetection object chemical substance, the desired detection objectchemical substance can be efficiently subjected to fragmentation.Accordingly, almost all the fragments of the detection object chemicalsubstance can be subjected to measurement of the mass analyzer, andtherefore the detection sensitivity of the mass analyzer can be improvedand the combustion can be controlled with higher precision. The TICKLEis an operation for subjecting a detection object chemical substance tofragmentation and separating the detection object chemical substancefrom an impurity having a mass number close to that of the detectionobject chemical substance. See “Development of a CapillaryHigh-Performance Liquid Chromatography Tandem Mass Spectrometry SystemUsing SWIFT Technology in an Ion Trap/Reflectron Time-of-flight MassSpectrometer”, Rapid Communication in mass spectrometry, vol. 111739–1748 (1997), for details.

In the chemical substance detection apparatus, the ionization unitapplies to the chemical substance energy higher than the ionizationpotential and equal to or smaller than a value of a sum of theionization potential and 4 electron volts. Furthermore, the ionizationunit is a light generation unit that generates light having a wavelengthof 50 to 200 nanometers. Moreover, the ionization unit is a vacuumultraviolet lamp.

It is preferable that the energy applied to the detection objectchemical substance by the ionization unit is higher than the ionizationpotential and equal to or smaller than a value of a sum of theionization potential and 4 electron volts. When the detection objectchemical substance is ionized by energy of light, the wavelength of thelight is 50 to 200 nanometers. Such a light is preferred since it can beeasily obtained using a vacuum ultraviolet lamp.

A chemical substance detection apparatus according to still anotheraspect of the present invention includes an ion trapping unit thattraps, using any one of an electric field and a magnetic field, an iongroup comprising ions of a chemical substance formed by ionization; anarbitrary waveform generation unit that generates a SWIFT waveformhaving a voltage amplitude in a frequency corresponding to an orbitalresonance frequency of an impurity present in a concentration such thatit exhibits a signal intensity higher than a predetermined signalintensity, wherein the voltage amplitude is larger than a voltageamplitude in a frequency band corresponding to an orbital resonancefrequency of the impurity present in a concentration such that itexhibits a signal intensity lower than a predetermined signal intensity;and a mass analyzer that applies the SWIFT waveform generated in thearbitrary waveform generation unit to the ion group trapped by the iontrapping unit to remove the impurity, and then measures a mass of thechemical substance or a fragment thereof.

In the chemical substance detection apparatus according to theabove-mentioned aspect, an impurity in an especially high concentrationcan be selectively removed by using a SWIFT waveform in which thevoltage amplitude in a frequency corresponding to the mass number of animpurity present in a concentration higher than a specific signalintensity is increased and the voltage amplitude in a frequencycorresponding to the mass number of an impurity present in a lowerconcentration is lowered. Thus, an impurity can be selectively removedand therefore only small energy is required for SWIFT. In addition, apower source apparatus can be reduced in size, and there is no need touse an excessively high power source and this is advantageous from aneconomical point of view. It is preferred that the impurity for whichthe voltage amplitude of a SWIFT waveform is increased is an impuritypresent in such a concentration that it exhibits at least a signalintensity substantially equivalent to the signal intensity of thedetection object chemical substance. The impurity may be an impuritypresent in a further smaller mass number, but larger energy is requiredfor SWIFT in such a case, and therefore it is preferred that theimpurity is an impurity having a signal intensity 50 percent or more ofthe signal intensity of the detection object chemical substance.

A chemical substance detection apparatus according to still anotheraspect of the present invention includes an ion trapping unit thattraps, using any one of an electric field and a magnetic field, an iongroup comprising ions of a chemical substance formed by ionization; anarbitrary waveform generation unit that generates a SWIFT waveform inwhich a voltage amplitude is reduced as a frequency is increased; and amass analyzer that applies the SWIFT waveform to the ion group trappedby the ion trapping unit to remove the impurity, and then measures amass of the chemical substance or a fragment thereof.

In the chemical substance detection apparatus according to theabove-mentioned aspect, the energy applied to an impurity having alarger mass number is higher than the energy applied to an impurityhaving a smaller mass number. Generally, the orbital resonance frequencyin an ion trap is a function of a mass number, and, the larger the massnumber, the smaller the frequency, or the smaller the frequency intervalcorresponding to the mass number interval 1. On the other hand, in theformation of a SWIFT waveform generally conducted in, for example, theliterature, “Development of a Capillary High-Performance LiquidChromatography Tandem Mass Spectrometry System Using SWIFT Technology inan Ion Trap/Reflectron Time-of-flight Mass Spectrometer”. RapidCommunication in mass spectrometry, vol. 11 1739–1748 (1997), a SWIFTwaveform is formed by subjecting a frequency spectrum having a fixedvoltage amplitude to inverse Fourier transform to convert it to a timeregion. In this case, a waveform synthesized from waveforms having afixed voltage amplitude at fixed frequency intervals is formed.Therefore, in this case, the larger the mass number, the smaller thenumber of the sinusoidal wave per mass number interval 1, and henceenergy per mass number interval 1 is small. In other words, the energyapplied to a molecule having a larger mass number becomes relativelysmall.

By contrast, in the chemical substance detection apparatus according tothe above-mentioned aspect, the voltage amplitude of the sinusoidal waveis increased for making up for the reduced number of the sinusoidalwave, and therefore satisfactory energy can be also applied to ionshaving large mass numbers, so that even such impurities can be surelyremoved. In addition, energy in a required and satisfactory range can beapplied to ions having small mass numbers and therefore the useefficiency of the energy can be improved. Further, an excessively highpower source apparatus is not required, and hence the cost for theapparatus can be suppressed.

A chemical substance detection apparatus according to still anotheraspect of the present invention includes an ion trapping unit thattraps, using any one of an electric field and a magnetic field, an iongroup comprising ions of a chemical substance formed by ionization; anarbitrary waveform generation unit that generates a SWIFT waveform inwhich a voltage amplitude has a fixed distribution, irrespective of amass number of a molecule to be removed by SWIFT; and a mass analyzerthat applies the SWIFT waveform to the ion group trapped by the iontrapping unit to remove an impurity, and then measures a mass of thechemical substance or a fragment thereof.

The chemical substance detection apparatus according to theabove-mentioned aspect is such that, when the frequency spectrum of aSWIFT waveform in which the voltage amplitude is increased as thefrequency is smaller is converted so that the mass number is taken as anabscissa, the voltage amplitude per unit mass number is a substantiallyfixed value. Thus, substantially the same energy can be applied tomolecules having any masses to be removed by SWIFT. Therefore,satisfactory energy can be also applied to ions having large massnumbers, and hence even such impurities can be surely removed. Further,an excessively high power source apparatus is not required, and hencethe cost for the apparatus can be suppressed.

A chemical substance detection apparatus according to still anotheraspect of the present invention includes an ion trapping unit thattraps, using any one of an electric field and a magnetic field, an iongroup comprising ions of a chemical substance formed by ionization; anarbitrary waveform generation unit that generates a SWIFT waveform whichgives no voltage amplitude in a plurality of frequency bandscorresponding to mass numbers of a plurality of chemical substances, andwhich gives a voltage amplitude in a frequency band corresponding to amass number of an impurity; a fragmentation unit that applies energy tothe ion group by means of a TICKLE waveform having a plurality offrequency components corresponding to orbital resonance frequencies ofthe chemical substances to fragmentate the ions of the chemicalsubstances; and a mass analyzer that applies the SWIFT waveform to theion group trapped by the ion trapping unit to remove the impurity, andthen measuring masses of the chemical substances or fragments thereof.

The amount of a dioxin or a precursor thereof contained in the exhaustgas from an incineration furnace is very slight, and an improvement ofthe detection accuracy therefor is very important when the conditionsfor combustion of the incineration furnace are controlled in real time.In the chemical substance detection apparatus according to the presentinvention, an impurity is removed using a SWIFT waveform which gives novoltage amplitude in the frequency bands corresponding to a plurality ofdetection object chemical substances. In addition, the detection objectchemical substances are detected simultaneously by the mass analyzer.Thus, a plurality of detection object chemical substances are detectedsimultaneously and; therefore, a measurement with high accuracy can beachieved and the precision of the combustion control can be improved.

The chemical substance detection apparatus further includes anionization unit that applies to the chemical substance energy higherthan an ionization potential of the chemical substance and lower than asum of the ionization potential and dissociation energy of ions of thechemical substance to ionize the chemical substance. Moreover, theionization unit applies to the chemical substance energy higher than theionization potential and equal to or smaller than a value of a sum ofthe ionization potential and 4 electron volts.

In the chemical substance detection apparatus according to theabove-mentioned aspect, energy higher than the ionization potential ofthe detection object chemical substance and lower than the dissociationenergy is applied to the detection object chemical substance to ionizethe detection object chemical substance. Therefore, unnecessaryfragments are not generated, and the detection object chemical substanceto be left is allowed to remain unbroken, making it possible to improvethe detection sensitivity of the mass analyzer. By virtue of this effectas well as the above-mentioned action and effect obtained by thechemical substance detection apparatus, the detection sensitivity of themass analyzer is further improved, enabling a measurement with highaccuracy. In addition, the combustion of an incineration furnace can becontrolled with higher precision. Further, the SWIFT voltage can belowered, and therefore there is no need to prepare an excessively highpower source and the production cost for the apparatus can besuppressed.

A chemical substance detection method according to still another aspectof the present invention includes an ionization step of applying to achemical substance energy higher than an ionization potential of thechemical substance and lower than a sum of the ionization potential anddissociation energy of ions of the chemical substance to ionize thechemical substance; an ion trapping step of trapping, using any one ofan electric field and a magnetic field, an ion group comprising the ionsof the chemical substance formed by ionization at the ionization step;an impurity removing step of applying energy to the ion group by meansof a SWIFT waveform comprising a frequency component excluding afrequency corresponding to an orbital resonance frequency of the ions ofthe chemical substance to remove an impurity from the chemicalsubstance; and a mass analyzing step of measuring a mass of the chemicalsubstance.

In the chemical substance detection method according to theabove-mentioned aspect, when an impurity is to be removed, energy higherthan the ionization potential of a detection object chemical substanceand lower than the dissociation energy is applied to the detectionobject chemical substance. Therefore, an impurity can be removed whileallowing the detection object chemical substance to remain unbroken, andgeneration of unnecessary fragment ions can be considerably suppressedduring the removal of an impurity. Accordingly, the detection objectchemical substance to be left can be allowed to remain unbroken, makingit possible to improve the detection sensitivity of the mass analyzer.Further, a SWIFT waveform is merely applied for removing an impurity andhence, the impurity can be quickly removed. In addition, in theionization according to the present invention, only a very few fragmentsare generated and the amount of impurities to be removed in the step ofremoving an impurity is extremely small, so that the SWIFT voltage canbe lowered, and hence there is no need to prepare an excessively highpower source, and the production cost for the apparatus can besuppressed.

A chemical substance detection method according to still another aspectof the present invention includes an ionization step of applying to achemical substance energy higher than an ionization potential of thechemical substance and lower than a sum of the ionization potential anddissociation energy of ions of the chemical substance to ionize thechemical substance; an ion trapping step of trapping, using any one ofan electric field and a magnetic field, an ion group comprising the ionsof the chemical substance formed by ionization at the ionization step;an impurity removing step of applying energy to the ion group by meansof a SWIFT waveform comprising a frequency component excluding afrequency corresponding to an orbital resonance frequency of the ions ofthe chemical substance to remove an impurity from the chemicalsubstance; a fragmentation step of applying energy to the ion group bymeans of a TICKLE waveform comprising a frequency componentcorresponding to the orbital resonance frequency of the ions of thechemical substance to fragmentate the ions of the chemical substance;and a mass analyzing step of measuring a mass of a fragment of thechemical substance.

In the chemical substance detection method according to theabove-mentioned aspect, fragmentation of the detection object chemicalsubstance is conducted by applying a TICKLE waveform to the detectionobject chemical substance. Therefore, even when an impurity is presentin a frequency band corresponding to the mass number of the detectionobject chemical substance, the effect of the impurity can be removed toachieve an accurate measurement. In addition, only very few fragmentsare generated in the ionization and therefore, in the fragmentation of adetection object chemical substance, the desired detection objectchemical substance can be efficiently subjected to fragmentation.Accordingly, almost all the fragments of the detection object chemicalsubstance can be subjected to mass analysis, so that the detectionsensitivity of analysis in the mass analyzer can be improved. By thisdetection method, in controlling the conditions for combustion of anincineration furnace, the combustion can be controlled with higherprecision.

A chemical substance detection method according to still another aspectof the present invention includes an ion trapping step of trapping,using any one of an electric field and a magnetic field, an ion groupcomprising ions of a chemical substance formed by ionization; animpurity removing step of measuring a distribution of an impuritycontained in the ion group and applying to the ion group a SWIFTwaveform comprising a frequency component corresponding to an impuritypresent in a predetermined ratio or more to remove the impurity; and amass analyzing step of measuring a mass of the chemical substance or afragment thereof.

In the chemical substance detection method according to theabove-mentioned aspect, an impurity present in a predetermined ratio ormore is selectively removed. Therefore, the energy needed for removingthe impurity in a required and satisfactory amount is small, as comparedto the energy needed for removing all the impurities. Therefore, a powersource apparatus can be reduced in size and this is advantageous from aneconomical point of view. It is preferred that the impurity in apredetermined ratio is an impurity present with at least a signalintensity substantially equivalent to the signal intensity of thedetection object chemical substance. The impurity may be an impurityhaving a further smaller signal intensity, but larger energy is requiredfor SWIFT in such a case, and therefore it is preferred that theimpurity is an impurity having a signal intensity 50 percent or more ofthe signal intensity of the detection object chemical substance.

A chemical substance detection method according to still another aspectof the present invention includes an ion trapping step of trapping,using any one of an electric field and a magnetic field, an ion groupcomprising ions of a chemical substance formed by ionization; anarbitrary waveform generation step of generating a SWIFT waveform havinga voltage amplitude in a frequency corresponding to an orbital resonancefrequency of an impurity present in a concentration such that itexhibits a signal intensity higher than a predetermined signalintensity, wherein the voltage amplitude is larger than a voltageamplitude in a frequency band corresponding to an orbital resonancefrequency of the impurity present in a concentration such that itexhibits a signal intensity lower than a predetermined signal intensity;and a mass analyzing step of applying the SWIFT waveform generated inthe arbitrary waveform generation unit to the ion group trapped in theion trapping step to remove the impurity, and then measuring a mass ofthe chemical substance or a fragment thereof.

In the chemical substance detection apparatus according to theabove-mentioned aspect, the voltage amplitude of a SWIFT waveform in afrequency corresponding to the mass number of an impurity present in ahigh concentration such that it exhibits a signal intensity higher thana specific signal intensity is increased, and the voltage amplitude foran impurity in a low concentration is lowered. Therefore, an impurity inan especially high concentration can be selectively removed. An impuritycan be selectively removed and hence only small energy is required forSWIFT. Thus, only small energy is required for SWIFT, and a power sourceapparatus can be reduced in size and there is no need to use anexcessively high power source, and this is advantageous from aneconomical point of view. It is preferred that the impurity for whichthe voltage amplitude of a SWIFT waveform is increased is an impurityhaving at least a signal intensity substantially equivalent to thesignal intensity of the detection object chemical substance. Theimpurity may be an impurity present in a further smaller mass number,but larger energy is required for SWIFT in such a case, and therefore itis preferred that the impurity is an impurity having a signal intensity50 percent or more of the signal intensity of the detection objectchemical substance.

A chemical substance detection method according to still another aspectof the present invention includes an ion trapping step of trapping,using any one of an electric field and a magnetic field, an ion groupcomprising ions of a chemical substance formed by ionization; animpurity removing step of applying a SWIFT waveform in which a voltageamplitude is reduced as a frequency is increased to remove an impurityfrom the chemical substance; and a mass analyzing step of measuring amass of the chemical substance or a fragment thereof.

In the chemical substance detection method according to the presentinvention, the energy applied to an impurity having a larger mass numberis higher than the energy applied to an impurity having a smaller massnumber. Generally, the orbital resonance frequency in an ion trap is afunction of a mass number, and, the larger the mass number, the smallerthe frequency, or the smaller the frequency interval corresponding tothe mass number interval 1. On the other hand, in the formation of aSWIFT waveform generally conducted in, for example, the literature“Development of a Capillary High-Performance Liquid ChromatographyTandem Mass Spectrometry System Using SWIFT Technology in an IonTrap/Reflectron Time-of-flight Mass Spectrometer”, Rapid Communicationin mass spectrometry, vol. 11 1739–1748 (1997), a SWIFT waveform isformed by subjecting a frequency spectrum having a fixed voltageamplitude to inverse Fourier transform to convert it to a time region.In this case, a waveform synthesized from waveforms having a fixedvoltage amplitude at fixed frequency intervals is formed. Therefore, inthis case, the larger the mass number, the smaller the number of thesinusoidal wave per mass number interval 1, and hence energy per massnumber interval 1 is small. In other words, the energy applied to amolecule having a larger mass number becomes relatively small.

By contrast, in the present invention, the voltage amplitude of thesinusoidal wave is increased for making up for the relatively smallenergy, and therefore satisfactory energy can be also applied to ionshaving large mass numbers, so that even such impurities can be surelyremoved. Further, an excessively high power source apparatus is notrequired, and hence the cost for the apparatus can be suppressed.

A chemical substance detection method according to still another aspectof the present invention includes an ion trapping step of trapping,using any one of an electric field and a magnetic field, an ion groupcomprising ions of a chemical substance formed by ionization; anarbitrary waveform generation step of generating a SWIFT waveform inwhich a voltage amplitude has a fixed distribution, irrespective of amass number of a molecule to be removed by SWIFT; and a mass analyzingstep of applying the SWIFT waveform to the ion group trapped at the iontrapping step to remove an impurity, and then measures a mass of thechemical substance or a fragment thereof.

This chemical substance detection method is such that, when thefrequency spectrum of a SWIFT waveform in which the voltage amplitude isincreased as the frequency is smaller is converted so that the massnumber is taken as an abscissa, the voltage amplitude per mass number isa substantially fixed value. Thus, substantially the same energy can beapplied to molecules having any masses to be removed by SWIFT.Therefore, satisfactory energy can be also applied to ions having largemass numbers, and hence even such impurities can be surely removed.Further, an excessively high power source apparatus is not required, andhence the cost for the apparatus can be suppressed.

A chemical substance detection method according to still another aspectof the present invention includes an ion trapping step of trapping,using any one of an electric field and a magnetic field, an ion groupcomprising ions of a chemical substance formed by ionization; a step ofapplying to the ion group a SWIFT waveform which gives no voltageamplitude in a plurality of frequency bands corresponding to massnumbers of a plurality of chemical substances to remove an impuritywhile leaving the chemical substances; and a mass analyzing step ofmeasuring masses of the chemical substances or fragments thereof.

The amount of a dioxin or a precursor thereof contained the exhaust gasfrom an incineration furnace is very slight, and an improvement of thedetection accuracy therefor is very important when the conditions forcombustion of the incineration furnace are controlled in real time. Inthe chemical substance detection method according to the presentinvention, an impurity is removed using a SWIFT waveform which gives novoltage amplitude in the frequency bands corresponding to a plurality ofdetection object chemical substances. In addition, the detection objectchemical substances are detected simultaneously by the mass analyzer.Thus, a plurality of detection object chemical substances are detectedsimultaneously and therefore, for example, even when the accuracy ofdetection of the individual detection object chemical substances isunsatisfactory, a plurality of substances are collectively examined fromthe correlation with dioxins or evaluated with respect to the combustionstate to achieve a measurement with higher accuracy, and the precisionof the combustion control can be improved.

A chemical substance detection method according to still another aspectof the present invention includes an ion trapping step of trapping,using any one of an electric field and a magnetic field, an ion groupcomprising ions of a plurality of chemical substances having differentmasses formed by ionization; a step of applying to the ion group a SWIFTwaveform which gives no voltage amplitude in a plurality of frequencybands corresponding to mass numbers of a plurality of chemicalsubstances to remove an impurity while leaving the chemical substances;and a fragmentation step of fragmenting the chemical substance in anorder of from a chemical substance having a smaller mass number to achemical substance having a larger mass number; a mass analyzing step ofmeasuring masses of the chemical substances or the fragments thereof.

In the chemical substance detection method according to the presentinvention, a plurality of detection object chemical substances aresuccessively subjected to fragmentation in the order of from a detectionobject chemical substance having a smaller mass number to those havinglarger one. Therefore, the fragmentation of the detection objectchemical substance having a small mass number makes it possible toprevent the fragment of a substance having a mass number larger thanthat of the detection object chemical substance from being broken. Thus,all the detection object chemical substances can be detected, so thatthe sensitivity of mass analysis can be improved to achieve ameasurement with higher accuracy.

A chemical substance detection method according to still another aspectof the present invention includes an ion trapping step of trapping,using any one of an electric field and a magnetic field, an ion groupcomprising ions of a plurality of chemical substances having differentmasses formed by ionization; a step of applying to the ion group a SWIFTwaveform which gives no voltage amplitude in a plurality of frequencybands corresponding to mass numbers of a plurality of chemicalsubstances to remove an impurity while leaving the chemical substances;and a fragmentation step of applying energy to at least two isotopes ofthe chemical substances by means of a TICKLE waveform comprisingfrequency components corresponding to the two isotopes to fragmentatethe two isotopes; and a mass analyzing step of measuring masses of thechemical substances or the fragments thereof.

In the chemical substance detection method according to the presentinvention, the chemical substance detection method applies a TICKLEwaveform comprising frequencies corresponding to at least two isotopesof the detection object chemical substance to subject at least twoisotopes of the detection object chemical substance to fragmentation,making mass analysis. Thus, a plurality of isotopes are used in the massanalysis and therefore, even when a dioxin or a precursor thereof ispresent in an extremely slight amount in the exhaust gas, the accuracyof detection can be improved. In addition, when used in controlling thecombustion of an incineration furnace, the precision of the control canbe improved.

In the chemical substance detection method, the mass analyzing stepincludes measuring at least two members among isotopes of fragmentsformed from the chemical substance.

In the chemical substance detection method according to the presentinvention, at least two isotopes of fragments formed from the detectionobject chemical substance are subjected to mass analysis. Thus, aplurality of isotopes of fragments are used in the mass analysis andtherefore, even when a dioxin or a precursor thereof is present in anextremely slight amount in the exhaust gas, the accuracy of detectioncan be improved. In addition, when used in controlling the combustion ofan incineration furnace, the precision of the control can be improved.

The chemical substance detection method further includes an ionizationstep of applying, before executing the ionization trap step, to thechemical substance energy higher than an ionization potential of thechemical substance and lower than a sum of the ionization potential anddissociation energy of ions of the chemical substance to ionize thechemical substance.

In the chemical substance detection method, the ionization step includesapplying to the chemical substance energy higher than the ionizationpotential and equal to or smaller than a value of a sum of theionization potential and 4 electron volts.

In the methods for detecting a chemical substance according to thepresent invention, energy higher than an ionization potential of adetection object chemical substance and lower than a sum of theionization potential and dissociation energy of ions of the detectionobject chemical substance is applied to the detection object chemicalsubstance to ionize the detection object chemical substance. Therefore,unnecessary fragments are not generated, and the detection objectchemical substance to be left is allowed to remain unbroken, making itpossible to improve the detection sensitivity of mass analysis. Byvirtue of this effect as well as the above-mentioned action and effectobtained by the chemical substance detection method, the detectionsensitivity of the mass analyzer is further improved, enabling ameasurement with high accuracy. In addition, the combustion of anincineration furnace can be controlled with higher precision. Further,the SWIFT voltage can be lowered, and therefore there is no need toprepare an excessively high power source and the production cost for theapparatus can be suppressed.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed descriptions of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view illustrating a chemical substancedetection apparatus according to the first embodiment of the invention;

FIG. 2 is a flowchart of a chemical substance detection method accordingto the first embodiment of the invention;

FIGS. 3A and 3B are explanatory diagrams of the ion signal intensitydistributions versus the RF voltage when the trap frequency is fixed;

FIGS. 4A and 4B are explanatory diagrams of the ion signal intensitydistributions versus the RF frequency when the RF voltage is fixed;

FIGS. 5A and 5B are diagrams explaining the relationship between a SWIFTfrequency and an amplitude and the relationship between an ion signaland a mass number;

FIG. 6 is a diagram explaining a frequency spectrum of a SWIFT waveformaccording to the fifth embodiment of the invention;

FIGS. 7A and 7B are diagrams explaining a frequency spectrum of aconventional SWIFT waveform;

FIGS. 8A and 8B are diagrams explaining a frequency spectrum of a SWIFTwaveform according to the sixth embodiment of the invention;

FIG. 9 is a diagram explaining a frequency spectrum of a SWIFT waveformaccording to the seventh embodiment of the invention;

FIGS. 10A and 10B are diagrams explaining a frequency spectrum of aTICKLE waveform according to the seventh embodiment of the invention;and

FIGS. 11A to 11D are diagrams explaining a frequency spectrum of aTICKLE waveform according to the ninth embodiment of the inventionwherein the diagrams are individually obtained by converting thefrequency spectrum so that the mass number is taken as an abscissa.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below with reference to theaccompanying drawings. The present invention, however, is not limited toexemplary embodiments. Further, elements in the exemplary embodimentsinclude ones that are easily conceived by persons skilled in the art orones substantially the same. In addition, elements in the exemplaryembodiments include ones that are easily conceived by persons skilled inthe art.

FIG. 1 is an explanatory view illustrating an chemical substancedetection apparatus according to the first embodiment of the presentinvention. An apparatus 100 for detecting a chemical substance includesan ionization chamber 1, a gas feeding apparatus 2, a vacuum ultravioletlamp 3 as an ionization unit, and a time-of-flight mass spectrometer 4as a mass analyzer. The ionization chamber 1 includes, as an iontrapping unit, an RF (radio frequency) ion trapping apparatus 10 havingan RF ring. The ionized detection object chemical substance in theexhaust gas is trapped in a trap 11 by means of a radio frequencyelectric field formed therein.

A unit that traps ions in the unit using an electric field, a magneticfield, or another electromagnetic force can be used. An electric field,a magnetic field, and other unit may be used individually or incombination appropriately. Several types of such ion trapping units areknown, and, of these, preferred is the RF ion trapping apparatus 11 inwhich a radio frequency electric field is formed since the handling ofthe apparatus is relatively easy. As the ion trapping unit other thanthe RF type, a Penning trap employing a direct voltage and a staticmagnetic field can be used.

The RF ion trapping apparatus 10 as the ion trapping unit includes afirst end cap 12, a second end cap 13, and an RF ring 14, and is of athree-dimensional tetrode type. As shown in FIG. 1, the RF ring 14 isdisposed inside of the first end cap 12 and the second end cap 13. Tothe RF ring 14 is connected a radio frequency power source apparatus 21for applying a trap voltage, which apparatus applies a radio frequencyvoltage as a trap voltage to the RF ring 14. The radio frequency appliedtraps in the trap 11 the ionized detection object chemical substance andother substances contained in the exhaust gas. An arbitrary waveformgeneration apparatus 20 as an arbitrary waveform generation unit isconnected to each of the first and second end caps 12, 13, and applies avoltage having a specific frequency to between the end caps in thebelow-described SWIFT and TICKLE.

The gas feeding apparatus 2 is provided with a gas injection pipe 5, andthe gas injection pipe 5 is formed from an on-off valve using anorifice, such as a pulse valve, or a capillary tube. Exhaust gas Gsfrom, for example, an incineration furnace, which is fed to the gasinjection pipe 5, is introduced into the ionization chamber 1. A heater6 is provided around the gas injection pipe 5. The heater 6 is a heatingapparatus for preventing a detection object chemical substance frombeing deposited on the inner wall of the gas injection pipe 5.

The ionization chamber 1 is provided with vacuum ultraviolet lamp 3 asan ionization unit that applies energy to a detection object chemicalsubstance to ionize it. The vacuum ultraviolet lamp 3 generates vacuumultraviolet light L by discharge of a gas obtained by adding a rare gas,such as Ar, Kr, or Xe, or H₂, O₂, or Cl₂ to Ar or He. In the presentembodiment, Lyman α light having a wavelength of 121.6 nanometers from ahydrogen plasma is used.

By changing the type of the gas discharged in the vacuum ultravioletlamp 3, the dose of the photon energy of the vacuum ultraviolet lightgenerated can be changed. Therefore, according to the ionizationpotential of a detection object chemical substance, there can be appliedphoton energy such that the detection object chemical substance does notundergo dissociation to an extent larger than that of the ionizationpotential. Thus, not only can ionization of the coexisting substancehaving an ionization potential higher than the photon energy beprevented, but also fragmentation of the detection object chemicalsubstance can be suppressed.

Instead of the vacuum ultraviolet lamp 3, a laser or its harmonics canbe used as the ionization unit. In this case, by using a tunable laser,a substance to be ionized can be selected by changing the photon energygenerated. As the tunable laser, a conventionally known one can be used.In the present invention, a vacuum ultraviolet light having a wavelengthof 50 to 200 nanometers can be used, and the wavelength of the light ismore preferably 100 to 200 nanometers, desirably in the range of from112 to 138 nanometers from the viewpoint of further suppressing thegeneration of unnecessary fragments.

As a unit that applies energy to a detection object chemical substanceto ionize it, a laser having the wavelength of a vacuum ultravioletlight, or an excimer lamp may be used. Alternatively, ions, for example,He ions may be accelerated by means of a particle accelerator andallowed to bombard a detection object chemical substance contained in asample gas in the ionization chamber 1. Further alternatively, electronbeams are separated in terms of a sector, and a beam having energy ofabout 10 electron volts is taken out and allowed to bombard a detectionobject chemical substance contained in the exhaust gas in the ionizationchamber 1.

The time-of-flight mass spectrometer 4 which is a mass analyzerspecifies a detection object chemical substance by measuring its masswith respect to the ions of the detection object chemical substancecontained in the exhaust gas, which ions are caused by ionization in theionization chamber 1. By applying a drawing voltage in a pulse form tothe second end cap 13 in the RF ion trapping apparatus 10, the ionizeddetection object chemical substance is introduced to the massspectrometer 4 and flies in the mass spectrometer 4. The flying ions aredetected by an ion detector 30, and the signal detected here isamplified by a preamplifier 31 and then taken in a data processingapparatus 32 and subjected to data processing. In the presentembodiment, a microchannel plate is used in the ion detector to improvethe sensitivity of ion detection. The mass spectrometer 4 measures atime of flight. There is a good correlation between a time of flight anda mass of the flying substance, and therefore a mass of the flyingsubstance is detected from a time of flight and the substance isidentified from the mass.

Procedures for detecting a precursor, which is a detection objectcontained in the exhaust gas, using an apparatus 100 for detecting achemical substance is described next with reference to FIG. 2. FIG. 2 isa flowchart of a chemical substance detection method according to thefirst embodiment of the present invention. First, exhaust gas Gs from anincineration furnace is fed to the ionization chamber 1 (step S101).Exhaust gas Gs fed to the ionization chamber 1 is then irradiated withvacuum ultraviolet light L from the vacuum ultraviolet lamp 3, so thatexhaust gas Gs receives photon energy from vacuum ultraviolet light L tobe ionized (step S102). The precursor as a detection object substancehas an ionization potential in the range of from 8.5 to 10.0 electronvolts. As mentioned above, the vacuum ultraviolet light used in thepresent embodiment has a wavelength of 121.6 nanometers, and its photonenergy is 10.1 electron volts. Energy slightly larger than theionization potential of the precursor is applied to the precursor, andhence the precursor can be ionized without applying thereto excessenergy.

Accordingly, the ionized precursor as a detection object chemicalsubstance can be efficiently subjected to measurement. The reason forthis resides in that the ionization using a vacuum ultraviolet lightgenerates only a very few fragments and almost all the ionized precursorcan be subjected to measurement by the mass spectrometer 4.Particularly, in the exhaust gas from an incineration furnace, aprecursor is present only in an extremely slight amount and thereforethis effect is remarkable. In addition, the lowering of the trappingefficiency of the trap 11 can be suppressed. When fragment ions arepresent in a large amount, the potential created by the ions trapped inthe trap 11 cancels the potential of the trap. However, the ionizationusing a vacuum ultraviolet light can considerably suppress generation ofunnecessary fragment ions, thus making it possible to suppress alowering of the trapping efficiency of the ion trap apparatus 11.

Further, the below-described SWIFT voltage can be lowered. The “SWIFT”means an operation for removing an impurity, in which a voltage waveformhaving a specific frequency is applied to between the first end cap 12and the second end cap 13 in the trap 11 to change the orbital of ions.In an ionization method that generates many fragments, a large number offragments having, as a parent molecule, the precursor which is adetection object chemical substance or another substance aredisadvantageously generated in the mass number which should be removedin the process of SWIFT. For removing them in SWIFT, a very largevoltage is required, and therefore a SWIFT voltage generation apparatus(arbitrary waveform generator) having a large power is needed. On theother hand, when the SWIFT voltage is increased, a molecule having amass number which is not intended to be broken is broken, together witha molecule having a mass number intended to be broken, and the precursorto be left is broken, leading to a lowering of the accuracy of massanalysis.

In the ionization according to the present invention, only a very fewfragments are generated, and therefore the number of fragments to beremoved in the process of SWIFT is extremely small. Accordingly, theSWIFT voltage can be lowered and the precursor to be left can be allowedto remain unbroken, so that almost all the problems can be solved. Whenthe parent molecule remaining after SWIFT is subjected to thebelow-described TICKLE or COOLING, fragments are generated from variousparent molecules in the ionization method that generates many fragments,so that fragments of substances other than the desired precursor arecontained as impurities, thus causing a lowering of the accuracy of massanalysis. By contrast, in the ionization method according to the presentinvention, only a few fragments are generated in the ionization, so thatthis problem can be substantially solved.

SWIFT is described next. This is an operation for removing unnecessarysubstances present in the exhaust gas while leaving a detection objectchemical substance. For this operation, a voltage at a frequency in awide band corresponding to an orbital resonance frequency of a substanceto be removed is applied by an arbitrary waveform generation apparatus20 to between the first end cap 12 and the second end cap 13 in the RFion trapping apparatus 10. This constitutes the impurity removing unitaccording to the present invention. The orbital resonance frequencycorresponding to the frequency of the mass number of the detectionobject chemical substance is excluded from the frequency in a wide band.The substance to be removed is vibrated with a large amplitude andbombards the wall of the RF ion trapping apparatus 10 to lose a charge,so that it is not present as an ion. The detection object chemicalsubstance is still trapped in the trap 11 by the trap voltage applied tothe RF ring 14. This operation is called SWIFT, and impurities can beremoved while leaving the detection object chemical substance by thisoperation (step S103).

TICKLE is described next. TICKLE is an operation for subjecting adetection object chemical substance to fragmentation and separating thedetection object chemical substance from an impurity having a massnumber close to the mass number of the detection object chemicalsubstance. Mass numbers of fragments generated from a molecule of thedetection object chemical substance as a parent molecule are thenmeasured to specify the detection object chemical substance. Further, bymeasuring the amount of the fragments, the concentration of thedetection object chemical substance can be determined. Different fromthe SWIFT, in TICKLE, a voltage at a frequency corresponding to theorbital resonance frequency of the detection object chemical substanceas a parent molecule is applied to between the first end cap 12 and thesecond end cap 13. In this case, a voltage at the frequency is appliedto between the end caps by means of the arbitrary waveform generationapparatus 20. This constitutes the fragmentation unit according to thepresent invention. The ions of the detection object chemical substanceare allowed to collide with other coexisting substances in the trap 11to fragmentate the detection object chemical substance, thus completingthe fragmentation by TICKLE (step S104).

After completion of the fragmentation by TICKLE, the application of thevoltage to the RF ring 14 is terminated, and a drawing voltage in apulse form is applied to the second end cap 13 to draw the fragment ionsof the detection object chemical substance to the mass spectrometer 4(step S105). The ions of the detection object chemical substance fly inthe mass spectrometer 4 and a time of flight is measured by the massspectrometer 4. As mentioned above, there is a good correlation betweena time of flight and a mass of the flying substance, and therefore amass of the flying substance is detected from a time of flight and thesubstance is identified from the mass (step S106), thus completing themeasurement (step S107).

The time-of-flight mass spectrometer used in the present embodiment hasadvantages in that one measurement operation is completed within severaltens microseconds, and the time required for measurement is very shortand the response is excellent. Therefore, the mass spectrometer ispreferred especially when the conditions for combustion in an actualplant are controlled in real time. As another mass analyzer, a massanalyzer of an electric field type or an RF coil type can be used.Particularly, the RF coil type can constitute a mass spectrometer havinga simple structure merely by providing an ion detector at the outlet ofthe trap 11.

In the apparatus 100 for detecting a chemical substance according to thepresent invention, the exhaust gas introduced to the trap 11 is directlyirradiated with vacuum ultraviolet light to ionize a substance to bemeasured. Ions of the substance to be measured are then subjected tofragmentation by SWIFT and TICKLE. For this reason, SWIFT orfragmentation may not be successfully achieved under the same conditionsas those for the conventional ionization. The conditions for SWIFT andTICKLE are described below. FIGS. 3A and 3B are explanatory diagrams ofthe ion signal intensity distributions versus the RF voltage when thetrap frequency is fixed. FIGS. 4A and 4B are explanatory diagrams of theion signal intensity distributions versus the RF frequency when the RFvoltage is fixed.

In the ionization conventionally used utilizing a unit other than vacuumultraviolet light, a detection object chemical substance is ionizedoutside of the trap 11. For fragmentation of the detection objectchemical substance, an inert gas or a bombardment gas, such as nitrogengas, is then fed into the trap 11 from the outside to fragmentate thedetection object chemical substance. Therefore, almost no air componentsincluding water vapor and oxygen contained in the exhaust gas as a gasto be measured are present in trap 11. For this reason, the ion signalintensity distributions shown in FIG. 3A and FIG. 4A are exhibited.

On the other hand, in the ionization method according to the presentinvention, the exhaust gas introduced to the trap 11 is directlyirradiated with vacuum ultraviolet light to ionize a detection objectchemical substance. Therefore, air components including water vapor andoxygen contained in the exhaust gas are present in the trap 11. When thedetection object chemical substance is subjected to fragmentation byapplying the below-described TICKLE voltage in an environment in whichsuch air component molecules including water vapor and oxygen coexistwith the detection object chemical substance, there may be presentconditions such that fragments cannot be trapped. For example, when theRF voltage exceeds 1500 volts, fragments cannot be trapped (FIG. 3B).Further, when the RF frequency is lower than 1.0 megahertz, fragmentscannot be trapped (FIG. 4B). The trap conditions mean values of the RFvoltage applied to the RF ring 14 and the RF frequency. The cause ofthis is presumed that water vapor, i.e., a water molecule and an oxygenmolecule have polarity and hence the orbital of the fragments of ions ofthe detection object chemical substance becomes larger, so that the ionsbombard the wall of the trap 11 to lose a charge.

For trapping the fragments of ions of the detection object chemicalsubstance even when the water molecule or oxygen molecule coexists withthe substance, it is necessary to adjust the trap conditions. Forexample, a case is presumed in which TCB (mass numbers: 180, 182, 184)is a parent molecule, and fragments (mass numbers: 145, 147) caused byelimination of one chlorine from the parent molecule, fragments (massnumbers: 109, 111) caused by elimination of two chlorines and onehydrogen, and a fragment (mass number: 74) caused by elimination ofthree chlorines and one hydrogen are detected. In a conventionalionization method, when the RF voltage is 1000 to 2000 volts at an RFfrequency of 1.0 megahertz, fragment ions can be advantageously trapped(see FIG. 3A).

Under the same frequency conditions in the presence of oxygen and watermolecules, when the RF voltage is 700 to 1300 volts, fragment ions canbe advantageously trapped, and, when the RF voltage is 900 to 1100volts, fragment ions can be more stably trapped (see FIG. 3B). When theRF voltage is 1600 volts, an RF frequency of 1.0 megahertz is suitablein the conventional method, but, in this method, when fragment ions canbe stably trapped at an RF frequency in the range of from 1.2 to 1.7megahertz. The fragment ions can be further stably trapped at an RFfrequency of 1.0 megahertz in the range of from 1.4 to 1.6 megahertz(see FIG. 4B).

In SWIFT, it is necessary to improve the trap efficiency of a substanceto be measured which is a parent molecule having a higher mass, whereas,in TICKLE, it is necessary to improve the trap efficiency of thefragments of the substance to be measured having lower mass numbers.Therefore, the value of energy applied to the RF ring 14 in SWIFT, i.e.,the product of an RF voltage and an RF frequency is adjusted to belarger. On the other hand, the product of an RF voltage and an RFfrequency in TICKLE is adjusted to be smaller. Thus, the trap efficiencyof the substance to be measured or fragments thereof in SWIFT and TICKLEcan be improved.

For example, the RF frequency is fixed at 1 megahertz, and trapping ismade at 1600 volts in SWIFT and at 1000 volts in TICKLE. Alternatively,the RF voltage may be fixed at 1600 volts, and trapping may be made atan RF frequency of 1.4 megahertz in SWIFT and at 1.0 megahertz inTICKLE. Further alternatively, both the RF frequency and the RF voltagemay be changed. This changing may be either in a stepwise responsemanner or in a gradual manner. The detection object chemical substancedissipates out of the trap 11 after a predetermined time of life haslapsed, and therefore it is advantageous that the conditions areoptimized so as to shorten the time required for TICKLE. Specifically,it is advantageous that the TICKLE voltage is higher.

The mass number of the detection object chemical substance after thefragmentation by TICKLE is smaller than that before the fragmentation.Therefore, it is at least necessary that the RF voltage applied to theRF ring 14 or the RF frequency after completion of TICKLE be smaller orlarger than that before TICKLE. However, when the RF voltage applied tothe RF ring 14 or the RF frequency is reduced or increased, the trapefficiency of the fragments having smaller mass numbers is lowered.Accordingly, when a certain period of time lapses in this state aftercompletion of TICKLE, such fragments are reduced to lower the detectionsensitivity of the mass spectrometer 4. Therefore, it is preferred toswitch the conditions as mentioned above immediately after a lapse ofthe time needed for fragmentation of the detection object chemicalsubstance after inputting a TICKLE waveform.

Substances other than a detection object chemical substance are removedin SWIFT, and, in this instance, an impurity having a mass numberequivalent to those of the fragment ions generated in the fragmentationof the detection object chemical substance must be removed. The reasonfor this is that such an impurity is detected together with the fragmentions in the mass analysis after the fragmentation by TICKLE to lower theaccuracy of measurement of the detection object chemical substance. Inaddition, when a large amount of other impurities are present in thetrap 11, the trap 11 is disadvantageously saturated to lower the trapefficiency, and therefore it is advantageous that almost all theimpurities are removed in SWIFT while leaving only the detection objectchemical substance.

For removing all the impurities while leaving only the detection objectchemical substance, a SWIFT waveform having frequency componentscorresponding to the mass numbers in a very wide range must be applied.However, such a SWIFT waveform having frequency components in a widerange has only small energy per unit frequency, and hence the energywhich can be applied to a molecule having a certain mass number isdisadvantageously small, so that the removal efficiency of impurities islowered, thus lowering the accuracy of detection of the detection objectchemical substance. Accordingly, when a SWIFT waveform having frequencycomponents in a wide range is applied, it is necessary to improve theperformance of the radio frequency generation apparatus 21 which is aSWIFT waveform source, to increase the output of an amplifier foramplifying the output of the radio frequency generation apparatus, or toexpand the band of the frequency amplified, so that the size of or costfor the apparatus is disadvantageously increased.

For solving the problem, a mass spectrum is measured with respect to theimpurities contained in the exhaust gas, and the impurities are removedby means of a SWIFT waveform having frequency components correspondingto the range of mass numbers which at least must be removed. The rangeof mass numbers which at least must be removed can be determined by, forexample, letting a mass spectrum include impurities having a value ofsignal intensity of the mass spectrum equal to or higher than apredetermined value. The predetermined value is at least substantiallyequivalent to the signal intensity of the chemical substance to bemeasured, and it is preferred that the impurities removed are impuritieshaving signal intensities equal to or higher than this value. Theimpurities removed may be impurities with further smaller mass numbers,but larger energy is required for SWIFT in such a case. Therefore, it ispreferred that the impurities are impurities having signal intensities50 percent or more of the signal intensity of the chemical substance tobe measured.

In an incineration furnace as an example, the range of mass numberswhich at least must be removed is, for example, 48 to 355, andimpurities are removed by means of a SWIFT waveform having frequencycomponents corresponding to this range. By this method, a measurement ofa detection object chemical substance with satisfactory accuracy from apractical point of view can be achieved without applying excessivelylarge energy to the trap 11. Thus, there is no need to use anexcessively large apparatus, and the cost for the apparatus can besuppressed.

FIGS. 5A and 5B are diagrams explaining the relationship between a SWIFTfrequency and an amplitude and the relationship between an ion signaland a mass number. The mass number shown in FIGS. 5A and 5B correspondsto the SWIFT frequency in the same figure. FIG. 6 is a diagramexplaining a frequency spectrum of a SWIFT waveform according to thefifth embodiment of the present invention. The frequency spectrum showsan intensity (voltage amplitude) of a SWIFT waveform or a TICKLEwaveform as a function of a frequency of the SWIFT or TICKLE waveform.For removing an impurity in a very high concentration, a very high SWIFTvoltage must be applied, but, in the conventional SWIFT, frequenciescorresponding to all the mass numbers are applied at the same voltageamplitude. Specifically, the SWIFT voltage is determined from thevoltage required for removing an impurity in the highest concentration.For this reason, when removing an impurity in a very high concentration,a very high voltage amplitude is needed as a whole, thus lowering theuse efficiency of energy.

In addition, a power source apparatus having a large capacity isrequired, increasing the cost. Further, for leaving a parent moleculewhich is a detection object chemical substance, the frequency bandcorresponding to the mass number of the detection object chemicalsubstance is excluded from the SWIFT waveform, but, when a high voltageamplitude is applied, the range of the mass numbers actually remainingafter excluding the frequency band is smaller than intended, so thatpart of the detection object chemical substance is removed, causing aproblem in that the detection accuracy is lowered. The reason for thisresides in that the actual frequency spectrum of a SWIFT waveform is notan ideal rectangular form indicated by the solid line shown in FIG. 5Abut a rectangular form which slightly broadens toward the bottomindicated by the broken line shown in FIG. 5B. Specifically, thefrequency spectrum of a SWIFT waveform is actually in a rectangular formwhich broadens toward the bottom, and therefore the frequency bandcorresponding to the mass number of the detection object chemicalsubstance indicated by AF shown in the figures becomes narrower, so thatthe detection accuracy is lowered.

Therefore, as shown in FIG. 6, the voltage amplitude of the SWIFTwaveform having a frequency corresponding to the mass number of animpurity in a high concentration is increased and the voltage amplitudefor the portion of an impurity in a low concentration is lowered. Thus,an impurity in an especially high concentration can be selectivelyremoved. It is preferred that the impurity of which the voltageamplitude of a SWIFT waveform is increased is an impurity having asignal intensity at least equivalent to the signal intensity of achemical substance to be measured. The impurity may be an impuritypresent in a further smaller mass number, but larger energy is requiredfor SWIFT in such a case. Therefore, it is preferred that the impurityis an impurity having a signal intensity 50 percent or more of thesignal intensity of the chemical substance to be measured. Thus, thevoltage amplitude of the SWIFT waveform can be lowered as a whole, sothat an impurity can be removed with increased use efficiency of energy.In addition, a power source apparatus having a small capacity can beused, and hence the power source apparatus can be reduced in size andthe cost can be lowered. Further, the detection object chemicalsubstance can be surely left in the SWIFT operation, thus making itpossible to improve the detection accuracy of the mass spectrometer 4.

FIGS. 3A and 3B are diagrams explaining a frequency spectrum of aconventional SWIFT waveform. FIGS. 8A and 8B are diagrams explaining afrequency spectrum of a SWIFT waveform according to the sixth embodimentof the present invention. FIGS. 7A and 8B are individually obtained byconverting the frequency spectrum of a SWIFT waveform so that the massnumber is taken as an abscissa, namely, a diagram as a function of themass number. A general SWIFT waveform is formed by subjecting to inverseFourier transform a rectangular-form frequency spectrum of which theamplitude is not changed even when the resonance frequency of ionsbecomes larger (FIG. 7A). The SWIFT waveform in this case is a waveformon which the resonance frequency corresponding to the mass number of animpurity to be removed superpose. This waveform is ideally a continuouswaveform including whole of the orbital resonance frequenciescorresponding to a certain mass range. However, the actual inverseFourier transform is made based on data of limited resonancefrequencies, and the resultant SWIFT waveform includes discretefrequency components and the frequency pitch is constant. When thiswaveform is represented in terms of a mass number, the frequency pitchis larger in a region in which the mass number is large, and thefrequency pitch is smaller in a region in which the mass number issmall.

When using such a SWIFT waveform, an amplitude at a high energy densityis applied to an ion having a smaller mass number, but an amplitude atonly a low energy density is applied to an ion having a larger massnumber (FIG. 7B). For this reason, an ion having a smaller mass numbercan be easily broken, but an ion having a larger mass number isdifficult to be broken, and thus it is left as an impurity. Unnecessaryfragments are generated by TICKLE to lower the accuracy of massanalysis.

For solving this problem, a SWIFT waveform formed by subjecting toinverse Fourier transform a frequency spectrum in which the voltageamplitude is reduced as the resonance frequency corresponding to themass number of an ion becomes higher is used (FIG. 8A). By using such aSWIFT waveform, satisfactory energy can be also applied to an ion havinga larger mass number (FIG. 8B). Specifically, there can be applied aSWIFT waveform in which the voltage amplitude has a fixed distribution,irrespective of the mass number of a molecule to be removed by SWIFT(FIG. 8B), so that even an ion having a larger mass number can befurther surely removed. Further, required and satisfactory energy can beapplied to an ion having a smaller mass number, so that the useefficiency of energy can be improved. In addition, an excessively largepower source apparatus is not required, and therefore the cost for theapparatus can be suppressed.

FIG. 9 is a diagram explaining a frequency spectrum of a SWIFT waveformaccording to the seventh embodiment of the present invention. FIGS. 10Aand 10B are diagrams explaining a frequency spectrum of a TICKLEwaveform according to the seventh embodiment of the present invention.In the measurement by means of the apparatus 100 for detecting achemical substance with respect to a detection object chemical substancewhich is, for example, a precursor of a dioxin, when a plurality ofdetection object chemical substances are simultaneously subjected tomeasurement, the detection accuracy can be further improved.Particularly, the amount of the precursor of a dioxin contained in theexhaust gas from an incineration furnace is extremely slight, and hencean improvement of the detection accuracy is very important when theconditions for combustion of the incineration furnace are controlled inreal time.

For subjecting a plurality of detection object chemical substances tomeasurement simultaneously, there is used in SWIFT a frequency spectrumof a SWIFT waveform in which the voltage amplitude is 0, that is, aSWIFT waveform which gives no voltage amplitude in the resonancefrequency band corresponding to the mass numbers of the detection objectchemical substances (FIG. 9). The frequency spectrum of this SWIFTwaveform is then subjected to inverse Fourier transform to form a SWIFTwaveform. When SWIFT is conducted using the SWIFT waveform obtained bythe inverse transform, the detection object chemical substances arestill trapped in the trap 11 of ion trapping apparatus 10, and thereforethey can be separated from impurities.

The detection object chemical substances are then subjected tofragmentation by means of a TICKLE waveform formed by subjecting toinverse Fourier transform a TICKLE frequency spectrum having a largeramplitude in the frequency band corresponding to the mass numbers of thedetection object chemical substances (FIG. 10A). The resultant fragmentions of the detection object chemical substances are then measured bymeans of the mass spectrometer 4 (see FIG. 1) to identify the detectionobject chemical substances, so that their concentrations can bedetermined. Alternatively, TICKLE may be conducted using a TICKLEwaveform formed by subjecting to inverse Fourier transform a TICKLEfrequency spectrum having a large amplitude in the range encompassingwhole of the frequencies corresponding to the mass numbers of thedetection object chemical substances (FIG. 10B). Further alternatively,the frequencies corresponding to the mass numbers of the detectionobject chemical substances may be individually applied to the respectivesubstances successively.

As described above, when a plurality of detection object chemicalsubstances are simultaneously subjected to measurement, the detectionaccuracy can be advantageously improved. However, when the plurality ofdetection objects chemical substances are simultaneously subjected tomeasurement, the following problem arises. For example, a case isconsidered in which a fragment pattern having TCB (trichlorobenzene) andDCB (dichlorobenzene) as parent molecules is obtained at the same time.A difference between a mass number of 145 of the TCB fragment and a massnumber of 146 of the DCB fragment is as small as 1. Therefore, when TCBand DCB are simultaneously subjected to TICKLE, part of the TCB fragmentmay be broken by the near TICKLE frequency of DCB. In such a case, forexample, a concentration of TCB cannot be determined by subjecting TCBto fragmentation and separating TCB from an impurity having a massnumber equivalent to the mass number of TCB to measure a signal of thefragment, so that the accuracy of detection of TCB is lowered. Thus, inthe TICKLE according to the seventh embodiment, various cares should betaken for accurately applying a frequency corresponding to the massnumber or optimizing the TICKLE voltage. In addition, even when suchcares are taken, the fragmentation may not be appropriately achieved.

For solving the problem, in the present embodiment, a detection objectchemical substance having a smaller mass number is first subjected tofragmentation by TICKLE, and another detection object chemical substanceor an impurity in the range of the mass number of the detection objectchemical substance is removed. A detection object chemical substancehaving a larger mass number is subjected to TICKLE to generate afragment of the detection object chemical substance having a larger massnumber in the range of the mass number in which the detection objectchemical substance having a smaller mass number is present.

By this method, when the detection object chemical substance having alarger mass number is subjected to fragmentation, the detection objectchemical substance having a smaller mass number has already beensubjected to fragmentation, preventing the fragment of the detectionobject chemical substance having a larger mass number from being brokenby the TICKLE for the detection object chemical substance having asmaller mass number. Accordingly, even when a plurality of detectionobject chemical substances having different mass numbers are detectedsimultaneously, a measurement with high accuracy can be achieved.

Specifically, a case is considered in which TCB (mass numbers: 180, 182,184, 186), DCB (mass numbers: 146, 148, 150), and MCB(monochlorobenzene; mass numbers: 112, 114) are detected simultaneously.Prior to TICKLE, impurities are removed by SWIFT while leaving thesedetection object chemical substances. For subjecting MCB tofragmentation, a TICKLE frequency corresponding to the mass number ofMCB is then applied to first and second end caps 12 and 13 to generate afragment having a mass number of 77. In this case, substances havingmass numbers of 112 to 114 are not present in the trap 11 of the iontrapping apparatus 10.

After the fragmentation of MCB, DCB is subjected to fragmentation byapplying a TICKLE frequency corresponding to the mass number of DCB. Theresultant fragments include ones having mass numbers of 111 and 113caused by elimination of one chlorine from DCB and one having a massnumber of 75 caused by elimination of two chlorines and one hydrogen.Finally, TCB is subjected to fragmentation by applying a frequencycorresponding to the mass number of TCB. The fragments generated in thisinstance include ones having mass numbers of 145, 147, and 149 caused byelimination of one chlorine, ones having mass numbers of 109 and 111caused by elimination of two chlorines and one hydrogen, and one havinga mass number of 74 caused by elimination of three chlorines and onehydrogen. The corresponding TICKLE frequencies are successively applied,respectively, to the fragments at certain intervals.

After completion of the fragmentation of the detection object chemicalsubstances, the fragment ions in the trap 11 are subjected to Coolingwithout applying a voltage to between the first and second end caps 12,13 in the ion trapping apparatus 10. The Cooling unit that the fragmentions collide with neutral gas in the trap 11 to lose their energy, andthe fragment ions are cooled by this procedure. The Cooling can improvethe accuracy of mass measurement by the mass spectrometer 4.

After completion of Cooling, a drawing voltage is applied to the secondend cap 13 to introduce the fragments to the mass spectrometer 4 and themasses of the fragments introduced are measured, so that theconcentrations of the detection object chemical substances can bedetermined. Specifically, the concentrations of MCB and DCB can bedetermined by selecting, respectively, the signal intensity of afragment having a mass number of 77 and the signal intensities offragments having mass numbers of 113 and 75. The concentration of TCBcan be determined by selecting the signal intensity of a fragment havinga mass number which does not overlap the fragments of MCB and DCB, forexample, a mass number of 145, 147, 149, 109, or 74.

Detection object chemical substances from which fragments generated havemass numbers which do not overlap, for example, TCB and TCP can besimultaneously broken by means of a TICKLE waveform. For example, MCBand MCP are first subjected to fragmentation, and then DCB and DCP, andfinally TCB and TCP are subjected to fragmentation, enabling asimultaneous measurement of six types of detection object chemicalsubstances. In this case, fragmentation is conducted two substances bytwo substances, and hence the time required for the fragmentation isonly about three times the time required for fragmentation for six typesof substances conducted one substance by one substance.

A detection object chemical substance may have an isotope, and such adetection object chemical substance has different mass numbers. Forexample, MCB has isotopes having mass numbers of 112 and 114. The reasonfor this is that the chlorine bonded to a benzene ring is of two typeshaving mass numbers of 35 and 37. In such a detection object chemicalsubstance having isotopes, the density of the detection object chemicalsubstance having one mass number is lower than the collective density ofthe detection object chemical substance, and therefore, when a substancehaving one mass number is solely subjected to measurement by means ofmass spectrometer 4, the sensitivity of measurement is disadvantageouslylowered.

Taking the MCB as an example, when MCB having a mass number of 112 issolely subjected to measurement, MCB having a mass number of 114 is notmeasured, so that the concentration actually detected is lower than thecollective concentration of MCB by the concentration of MCB having amass number of 114 which is not measured. Particularly, a precursor of adioxin contained in the exhaust gas from an incineration furnace, whichis a detection object chemical substance, has an extremely lowconcentration, and therefore it is necessary to improve the detectionsensitivity as high as possible.

By subjecting to fragmentation all of the isotopes of at least twodetection object chemical substances, the problem of a lowering of themeasurement sensitivity can be solved. An explanation is made below,with taking the isotopes of TCB as an example, but the present inventionis not limited to TCB, and any detection object chemical substances canbe applied as long as they have isotopes. FIGS. 11A to 11D are diagramsexplaining a frequency spectrum of a TICKLE waveform according to theninth embodiment of the present invention wherein the diagrams areindividually obtained by converting the frequency spectrum so that themass number is taken as an abscissa. FIG. 11A shows the distribution ofisotopes in TCB ions.

For example, all the isotopes of detection object chemical substancescan be subjected to fragmentation, an isotope having a theoreticallylower concentration can be removed from all the isotopes, or theisotopes of detection object chemical substances from which the massnumber having a larger impurity ratio is excluded can be subjected tofragmentation. In this case, as a TICKLE waveform, there can be used oneobtained by subjecting to inverse Fourier transform a frequency spectrumwhich gives a large amplitude in a wide range of a resonance frequencyband so as to include the mass numbers of all the isotopes of at leasttwo detection object chemical substances (FIG. 11B).

The mass number of which the resonance frequency affects ions hasvariation and therefore, when a frequency spectrum having a fixedamplitude is used, a phenomenon occurs in which TICKLE is difficult forthe isotopes having the maximum and minimum mass numbers and TICKLE isrelatively easy for the isotope having an intermediate mass number. Forthis reason, when using a frequency spectrum in which the voltageamplitude is large in the maximum and minimum mass numbers of theisotopes of the detection object chemical substance, all of theplurality of isotopes as the object of TICKLE can be subjected tosubstantially the same TICKLE, thus enabling substantially uniformfragmentation. Alternatively, there may be used a frequency spectrum inwhich the voltage amplitude is large in the maximum and minimum massnumbers of the isotopes as the object of fragmentation and the voltageamplitude is relatively small in the intermediate mass number (solidline in FIG. 11C). Further alternatively, there may be used a frequencyspectrum in which the voltage amplitude in the isotope having arelatively low ion signal intensity is smaller than the voltageamplitude in the isotope having a relatively high ion signal intensity(broken line in FIG. 11C).

On the other hand, a large amount of impurities having substantially thesame mass number as that of one certain isotope may be present. Forexample, it is presumed that, in FIG. 11D, a large amount of impuritieshaving the same mass number as that of a TCB isotope having a massnumber of 180 are present. In such a case, a plurality of isotopesexcluding this isotope may be subjected to fragmentation so that thelarge amount of impurities are not subjected to fragmentation, achievinga measurement with high accuracy. In this case, there can be used aTICKLE waveform obtained by subjecting to inverse Fourier transform afrequency spectrum comprising a plurality of resonance frequenciescorresponding to the mass numbers of a plurality of isotopes which donot contain impurities very much in the same mass number and which areselected from the isotopes (isotopes of TCB here) (FIG. 11D).

A detection object chemical substance has an isotope, and a fragment ofthe detection object chemical substance has an isotope similarly.Therefore, a measurement of the fragment has similar problems describedin connection with the eighth embodiment. Conventionally, theconcentration of a detection object chemical substance has been measuredonly from one fragment, or the concentration of a detection objectchemical substance has been estimated by pattern matching of fragments.

However, in a substance present only in an extremely low concentration,such as a precursor of a dioxin contained in the exhaust gas from anincineration furnace, when one isotope of a fragment is merely measured,a measurement with satisfactory sensitivity cannot be made. Even in thepattern matching of a plurality of fragments, the absolute number of thefragments in one isotope is too small and unsatisfactory forstatistically estimating the concentration.

For solving the problem, among the isotopes of the fragments formed froma detection object chemical substance, at least two isotopes aresubjected to measurement. Specifically, in a spectrum (signal voltage)of a certain fragment, a value of a sum of maximum values of thespectrum of a plurality of isotopes, or a value of a sum of areas of thespectrum of a plurality of isotopes is used as a measurement value ofmass spectrometer 4. By this method, all the isotopes of a certainfragment can be used, and therefore, even when the concentration of asubstance to be measured is extremely low, the sensitivity ofmeasurement by mass spectrometer 4 can be improved. In addition, when aspectrum having a large noise component is present, for example, animpurity fragment appears in the mass number of a certain isotope, themass number of the isotope excluding the spectrum of the isotope may beselected to determine the concentration of the substance to be measured,so that the noise of an impurity can be removed, thus enabling ameasurement with higher accuracy.

As described above, in the chemical substance detection apparatusaccording to the present invention, in ionization of a detection objectchemical substance, energy higher than an ionization potential of thedetection object chemical substance and lower than a sum of theionization potential and dissociation energy of ions of the detectionobject chemical substance is applied to the detection object chemicalsubstance. Therefore, the detection object chemical substance can beionized without being broken, and further, generation of unnecessaryfragments, which is a problem caused when removing an impurity by SWIFT,can be considerably suppressed. Accordingly, the detection objectchemical substance to be left is allowed to remain unbroken, making itpossible to improve the detection sensitivity of the mass analyzer.Further, a SWIFT waveform is merely applied for removing an impurity andhence, the impurity can be quickly removed. Thus, the rate of detectionof the detection object chemical substance can be increased and hence itis preferred in the control of an actual incineration furnace.

In the chemical substance detection apparatus according to the presentinvention, fragmentation of the detection object chemical substance isperformed by means of a fragmentation unit that applies a TICKLEwaveform. Therefore, even when an impurity is present in a frequencyband corresponding to the mass number of the detection object chemicalsubstance, the effect of the impurity can be removed to achieve anaccurate measurement. In addition, only a very few fragments aregenerated in the ionization and therefore, in the fragmentation of thedetection object chemical substance, the desired detection objectchemical substance can be efficiently subjected to fragmentation.Accordingly, the detection sensitivity of the mass analyzer can beimproved, and the combustion can be controlled with higher precision.

In the chemical substance detection apparatus according to the presentinvention, the energy applied to the detection object chemical substanceby the ionization unit is higher than the ionization potential and equalto or smaller than a value of a sum of the ionization potential and 4electron volts. When the detection object chemical substance is ionizedby energy of light, the wavelength of the light is 50 to 200 nanometers.Therefore, an impurity can be removed without generating unnecessaryfragments. In addition, a vacuum ultraviolet lamp is used for suchlight, and hence the handling is easy and the construction of theapparatus can be simplified.

In the chemical substance detection apparatus according to the presentinvention, the voltage amplitude of a SWIFT waveform in a frequencycorresponding to the mass number of an impurity present in a highconcentration such that it exhibits a signal intensity higher than aspecific signal intensity is increased, and the voltage amplitude for animpurity in a low concentration is lowered. Therefore, an impurity in anespecially high concentration can be selectively removed. An impuritycan be selectively removed and hence only small energy is required forSWIFT. Thus, a power source apparatus can be reduced in size, and thereis no need to use an excessively high power source and this isadvantageous from an economical point of view.

In the chemical substance detection apparatus according to the presentinvention, the energy applied to an impurity having a larger mass numberis higher than the energy applied to an impurity having a smaller massnumber. Further, the chemical substance detection apparatus according tothe present invention is such that, when the frequency spectrum of aSWIFT waveform in which the voltage amplitude is increased as thefrequency is smaller is converted so that the mass number is taken as anabscissa, the voltage amplitude per unit mass number is a substantiallyfixed value. Therefore, satisfactory energy is applied to an impurityhaving a larger mass number to remove it and energy in a required andsatisfactory range can be applied to ions having small mass numbers, andthus the use efficiency of the energy can be improved, so that anexcessively high power source apparatus is not required and hence thecost for the apparatus can be suppressed.

In the chemical substance detection apparatus according to the presentinvention, an impurity is removed using a SWIFT waveform which gives novoltage amplitude in the frequency bands corresponding to a plurality ofdetection object chemical substances. In addition, the detection objectchemical substances are detected simultaneously by the mass analyzer.Thus, a plurality of detection object chemical substances are detectedsimultaneously and therefore, a measurement with high accuracy can beachieved and the precision of the combustion control can be improved.

In the chemical substance detection apparatus according to the presentinvention, the chemical substance detection apparatus further includesan ionization unit that applies to the detection object chemicalsubstance energy higher than an ionization potential of the detectionobject chemical substance and lower than a sum of the ionizationpotential and dissociation energy of ions of the detection objectchemical substance to ionize the detection object chemical substance. Inthe chemical substance detection apparatus according to the presentinvention, the ionization unit in the chemical substance detectionapparatus applies to the detection object chemical substance energyhigher than the ionization potential and equal to or smaller than avalue of a sum of the ionization potential and 4 electron volts. Inthese apparatuses for detecting a chemical substance according to thepresent invention, energy higher than the ionization potential of thedetection object chemical substance and lower than a sum of theionization potential and dissociation energy of ions of the detectionobject chemical substance is applied to the detection object chemicalsubstance to ionize the detection object chemical substance. Therefore,unnecessary fragments are not generated, and the detection objectchemical substance to be left is allowed to remain unbroken, making itpossible to improve the detection sensitivity of the mass analyzer. Byvirtue of this effect as well as the above-mentioned action and effectobtained by the chemical substance detection apparatus, the detectionsensitivity of the mass analyzer is further improved, enabling ameasurement with high accuracy.

In the chemical substance detection method according to the presentinvention, in ionization, energy higher than an ionization potential ofa detection object chemical substance and lower than a sum of theionization potential and dissociation energy of ions of the detectionobject chemical substance is applied to the detection object chemicalsubstance. Therefore, the detection object chemical substance can beionized without being broken, and further, generation of unnecessaryfragments can be considerably suppressed in the ionization. Accordingly,the detection object chemical substance to be left can be allowed toremain unbroken, making it possible to improve the detection sensitivityof the mass analyzer.

In the chemical substance detection method according to the presentinvention, fragmentation of the detection object chemical substance isconducted by applying a TICKLE waveform to the detection object chemicalsubstance. Therefore, even when an impurity is present in a frequencyband corresponding to the mass number of the detection object chemicalsubstance, the effect of the impurity can be removed to achieve anaccurate measurement. Accordingly, almost all the fragments of thedetection object chemical substance can be subjected to mass analysis,so that the detection sensitivity of analysis in the mass analyzing stepcan be improved.

In the chemical substance detection method according to the presentinvention, an impurity present in a predetermined ratio or more isselectively removed. Therefore, the energy needed for removing theimpurity in a required and satisfactory amount is small, as compared tothe energy needed for removing all the impurities. Only small energy isneeded, and hence a power source apparatus can be reduced in size andthis is advantageous from an economical point of view.

In the chemical substance detection method according to the presentinvention, the voltage amplitude of a SWIFT waveform in a frequencycorresponding to an impurity having a signal intensity higher than aspecific signal intensity is increased, and the voltage amplitude in afrequency corresponding to an impurity in a low concentration islowered. Therefore, an impurity in an especially high concentration canbe selectively removed, and the energy required for removing an impurityin a low concentration can be reduced. Thus, only small energy isrequired for removing an impurity, and there is no need to use anexcessively high power source and this is advantageous from aneconomical point of view.

In the chemical substance detection method according to the presentinvention, the energy applied to an impurity having a larger mass numberis higher than the energy applied to an impurity having a smaller massnumber. Further, the chemical substance detection method according tothe present invention is such that, when the frequency spectrum of aSWIFT waveform in which the voltage amplitude is increased as thefrequency is smaller is converted so that the mass number is taken as anabscissa, the voltage amplitude per mass number is a substantially fixedvalue. Therefore, satisfactory energy is applied to an impurity having alarger mass number to remove it and energy in a required andsatisfactory range can be applied to ions having small mass numbers, andthus the use efficiency of the energy can be improved, so that anexcessively high power source apparatus is not required and hence thecost for the apparatus can be suppressed.

In the chemical substance detection apparatus according to the presentinvention, an impurity is removed using a SWIFT waveform which gives novoltage amplitude in the frequency bands corresponding to a plurality ofdetection object chemical substances. In addition, the detection objectchemical substances are detected simultaneously by the mass analyzer.Thus, a plurality of detection object chemical substances are detectedsimultaneously and therefore, a measurement with high accuracy can beachieved and the precision of the combustion control can be improved.

In the chemical substance detection method according to the presentinvention, a plurality of detection object chemical substances aresuccessively subjected to fragmentation in the order of from a detectionobject chemical substance having a smaller mass number to those havinglarger one. Therefore, all the detection object chemical substances canbe detected and hence the sensitivity of mass analysis is improved,enabling a measurement with higher accuracy.

In the chemical substance detection method according to the presentinvention, the chemical substance detection method applies a TICKLEwaveform comprising frequencies corresponding to at least two isotopesof the detection object chemical substance to subject at least twoisotopes of the detection object chemical substance to fragmentation,making mass analysis. Thus, a plurality of isotopes are used in the massanalysis and therefore, even when a dioxin or a precursor thereof ispresent in an extremely slight amount in the exhaust gas, the accuracyof detection can be improved.

In the chemical substance detection method according to the presentinvention, at least two isotopes of fragments formed from the detectionobject chemical substance are subjected to mass analysis. Thus, aplurality of isotopes of fragments are used in the mass analysis andtherefore, even when a dioxin or a precursor thereof is present in anextremely slight amount in the exhaust gas, the accuracy of detectioncan be improved.

In the chemical substance detection method according to the presentinvention, before the ion trapping step in the chemical substancedetection method, energy higher than an ionization potential of thedetection object chemical substance and lower than a sum of theionization potential and dissociation energy of ions of the detectionobject chemical substance is applied to the detection object chemicalsubstance to ionize the detection object chemical substance. In thechemical substance detection method according to the present invention,in the ionization step, energy higher than the ionization potential andequal to or smaller than a value of a sum of the ionization potentialand 4 electron volts is applied to the detection object chemicalsubstance. Therefore, unnecessary fragments are not generated, and thedetection object chemical substance to be left is allowed to remainunbroken, making it possible to improve the detection sensitivity ofmass analysis. By virtue of this effect as well as the above-mentionedaction and effect obtained by the chemical substance detection method,the detection sensitivity of the mass analyzer is further improved,enabling a measurement with high accuracy.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

INDUSTRIAL APPLICABILITY

As mentioned above, the chemical substance detection apparatus and thechemical substance detection method according to the present inventionare useful for detecting, with high accuracy, a dioxin or a precursorthereof contained in a very slight amount in the exhaust gas from, e.g.,a refuse incineration system, and suitable for improving the rate ofdetection of a chemical substance to be detected to such an extent thatthe combustion conditions of a combustion furnace, such as a heatingfurnace, can be controlled even during the operation of the furnace.

1. A chemical substance detection apparatus, comprising: an ion trappingunit that traps, using any one of an electric field and a magneticfield, an ion group comprising ions of a chemical substance formed byionization; an arbitrary waveform generation unit that generates a SWIFTwaveform having a first voltage amplitude in a first frequency bandcorresponding to an orbital resonance frequency of a first impuritypresent in a concentration, a second voltage amplitude in a secondfrequency band corresponding to an orbital resonance frequency of asecond impurity present in the concentration, and zero voltage amplitudein a third frequency band corresponding to an orbital resonancefrequency of the chemical substance, wherein signal intensitiescorresponding to the first impurity and the second impurity are apredetermined signal intensity or larger, and wherein the first voltageamplitude is larger than the second voltage amplitude; and a massanalyzer that applies the SWIFT waveform generated in the arbitrarywaveform generation unit to the ion group trapped by the ion trappingunit to remove the impurities, and then measures a mass of the chemicalsubstance or a fragment thereof.
 2. The chemical substance detectionapparatus according to claim 1, further comprising an ionization unitthat applies to the chemical substance energy higher than an ionizationpotential of the chemical substance and lower than a sum of theionization potential and dissociation energy of ions of the chemicalsubstance to ionize the chemical substance.
 3. The chemical substancedetection apparatus according to claim 2, wherein the ionization unitapplies to the chemical substance energy higher than the ionizationpotential and equal to or smaller than a value of a sum of theionization potential and 4 electron volts.
 4. A chemical substancedetection apparatus, comprising: an ion trapping unit that traps, usingany one of an electric field and a magnetic field, an ion groupcomprising ions of a chemical substance formed by ionization; anarbitrary waveform generation unit that generates a SWIFT waveform inwhich a voltage amplitude is reduced as a frequency is increased; and amass analyzer that applies the SWIFT waveform to the ion group trappedby the ion trapping unit to remove the impurity, and then measures amass of the chemical substance or a fragment thereof.
 5. The chemicalsubstance detection apparatus according to claim 4, further comprisingan ionization unit that applies to the chemical substance energy higherthan an ionization potential of the chemical substance and lower than asum of the ionization potential and dissociation energy of ions of thechemical substance to ionize the chemical substance.
 6. The chemicalsubstance detection apparatus according to claim 5, wherein theionization unit applies to the chemical substance energy higher than theionization potential and equal to or smaller than a value of a sum ofthe ionization potential and 4 electron volts.
 7. A chemical substancedetection method, comprising: an ion trapping step of trapping, usingany one of an electric field and a magnetic field, an ion groupcomprising ions of a chemical substance formed by ionization; anarbitrary waveform generation step of generating a SWIFT waveform havinga first voltage amplitude in a first frequency band corresponding to anorbital resonance frequency of a first impurity present in aconcentration, a second voltage amplitude in a second frequency bandcorresponding to an orbital resonance frequency of a second impuritypresent in the concentration, and zero voltage amplitude in a thirdfrequency band corresponding to an orbital resonance frequency of thechemical substance, wherein signal intensities corresponding to thefirst impurity and the second impurity are a predetermined signalintensity or larger, and wherein the first voltage amplitude is largerthan the second voltage amplitude; and a mass analyzing step of applyingthe SWIFT waveform generated in the arbitrary waveform generation stepto the ion group trapped in the ion trapping step to remove theimpurities, and then measuring a mass of the chemical substance or afragment thereof.
 8. The chemical substance detection method accordingto claim 7, wherein the mass analyzing step includes measuring at leasttwo members among isotopes of fragments formed from the chemicalsubstance.
 9. The chemical substance detection method according to claim7, further comprising an ionization step of applying, before executingthe ionization trap step, to the chemical substance energy higher thanan ionization potential of the chemical substance and lower than a sumof the ionization potential and dissociation energy of ions of thechemical substance to ionize the chemical substance.
 10. The chemicalsubstance detection method according to claim 9, wherein the ionizationstep includes applying to the chemical substance energy higher than theionization potential and equal to or smaller than a value of a sum ofthe ionization potential and 4 electron volts.
 11. A chemical substancedetection method, comprising: an ion trapping step of trapping, usingany one of an electric field and a magnetic field, an ion groupcomprising ions of a chemical substance formed by ionization; animpurity removing step of applying a SWIFT waveform in which a voltageamplitude is reduced as a frequency is increased to remove an impurityfrom the chemical substance; and a mass analyzing step of measuring amass of the chemical substance or a fragment thereof.
 12. The chemicalsubstance detection method according to claim 11, wherein the massanalyzing step includes measuring at least two members among isotopes offragments formed from the chemical substance.
 13. The chemical substancedetection method according to claim 11, further comprising an ionizationstep of applying, before executing the ionization trap step, to thechemical substance energy higher than an ionization potential of thechemical substance and lower than a sum of the ionization potential anddissociation energy of ions of the chemical substance to ionize thechemical substance.
 14. The chemical substance detection methodaccording to claim 13, wherein the ionization step includes applying tothe chemical substance energy higher than the ionization potential andequal to or smaller than a value of a sum of the ionization potentialand 4 electron volts.
 15. A chemical substance detection method,comprising: an ion tapping step of trapping, using any one of anelectric field and a magnetic field, an ion group comprising ions of aplurality of chemical substances having different masses formed byionization; a step of applying to the ion group a SWIFT waveform whichgives no voltage amplitude in a plurality of frequency bandscorresponding to mass numbers of a plurality of chemical substances toremove an impurity while leaving the chemical substances; afragmentation step of fragmenting the chemical substance in an order offrom a chemical substance having a smaller mass number to a chemicalsubstance having a larger mass number; and a mass analyzing step ofmeasuring masses of the chemical substances or the fragments thereof.16. The chemical substance detection method according to claim 15,wherein the mass analyzing step includes measuring at least two membersamong isotopes of fragments formed from the chemical substance.
 17. Thechemical substance detection method according to claim 15, furthercomprising an ionization step of applying, before executing theionization trap step, to the chemical substance energy higher than anionization potential of the chemical substance and lower than a sum ofthe ionization potential and dissociation energy of ions of the chemicalsubstance to ionize the chemical substance.
 18. The chemical substancedetection method according to claim 17, wherein the ionization stepincludes applying to the chemical substance energy higher than theionization potential and equal to or smaller than a value of a sum ofthe ionization potential and 4 electron volts.
 19. A chemical substancedetection method, comprising: an ion trapping step of trapping, usingany one of an electric field and a magnetic field, an ion groupcomprising ions of a plurality of chemical substances having differentmasses formed by ionization; a step of applying to the ion group a SWIFTwaveform which gives no voltage amplitude in a plurality of frequencybands corresponding to mass numbers of a plurality of chemicalsubstances to remove an impurity while leaving the chemical substances;and a fragmentation step of applying energy to at least two isotopes ofthe chemical substances by means of a TICKLE waveform comprisingfrequency components corresponding to the two isotopes to fragmentatethe two isotopes; and a mass analyzing step of measuring masses of thechemical substances or the fragments thereof.
 20. The chemical substancedetection method according to claim 19, wherein the mass analyzing stepincludes measuring at least two members among isotopes of fragmentsformed from the chemical substance.
 21. The chemical substance detectionmethod according to claim 19, further comprising an ionization step ofapplying, before executing the ionization trap step, to the chemicalsubstance energy higher than an ionization potential of the chemicalsubstance and lower than a sum of the ionization potential anddissociation energy of ions of the chemical substance to ionize thechemical substance.
 22. The chemical substance detection methodaccording to claim 21, wherein the ionization step includes applying tothe chemical substance energy higher than the ionization potential andequal to or smaller than a value of a sum of the ionization potentialand 4 electron volts.